feat: added reactivate_policy plus a get_deactivated_policies paginat…

[DTech-Wiz1]

Description

Completes the insurance policy lifecycle by introducing policy reactivation support and visibility into deactivated policies.

Previously, deactivate_policy removed a policy from ActivePolicies and marked it inactive, but the underlying policy record remained stored indefinitely with no way to reactivate it or enumerate inactive policies. This created a one-way state transition that forced integrators to create entirely new policies to recover from suspensions or administrative mistakes, resulting in lost continuity and reduced auditability.

This change introduces:

• reactivate_policy(env, caller, policy_id) to restore an inactive policy.
• get_deactivated_policies(env, owner, cursor, limit) for paginated retrieval of inactive policies owned by a specific user.
• PolicyReactivatedEvent for lifecycle observability.
• Shared active-set helper functions used by policy creation, deactivation, and reactivation to prevent duplication and ensure consistency.

Additional behavior:

• Reactivation is authorized for the same actors allowed to deactivate a policy (policy owner or contract owner).
• Reactivation sets active = true, refreshes next_payment_date, and safely re-adds the policy to ActivePolicies.
• Reactivation rejects already-active policies with a typed error.
• Reactivation rejects operations that would exceed MAX_POLICIES using MaxPoliciesReached.
• Active policy IDs cannot be duplicated in the active set.
• Added doc comments describing active ⇄ inactive transitions and policy-cap interactions.
• Updated EVENTS.md with PolicyReactivatedEvent documentation.

Closes #822

Type of Change

• feat — new functionality
• fix — bug fix
• docs — documentation only
• refactor — code restructuring with no behaviour change
• test — test additions or improvements
• ci — CI configuration changes
• chore — maintenance, dependencies, tooling

How Has This Been Tested?

• cargo test --workspace passes
• cargo fmt --all -- --check passes
• cargo clippy --workspace --all-targets --all-features -- -D warnings passes
• Coverage ≥ 95% for affected crates (cargo llvm-cov --package <crate> --fail-under-lines 95)
• Fuzz harness passes (cargo test -p credence_bond fuzz::test_bond_fuzz -- --nocapture)
• Error code wire-stability test passes (cargo test -p credence_errors error_codes_wire)
• Release build passes (cargo build --release)